package A01;
import java.util.Scanner;


public class D06 {
    public static void main (String[] args) {
        Scanner in=new Scanner (System.in);
        while(in.hasNextInt ()){
            int w=in.nextInt ();
            int h=in.nextInt ();
            int n1=w*h/4;
            int n2=w*h%4;
            int sum;
            if(n2<2)sum=n1*2+n2;
            else sum=n1*2+2;
            System.out.println (sum);
        }

    }
}
